1. Field of the Invention
The present invention relates generally to underground septic systems, and more particularly to a novel and improved flexible gasket for installing and positively sealing a pipe in an opening of a septic tank.
2. Description of the Prior Art
Septic tanks for domestic use are typically constructed of cast concrete, fiberglass or molded plastic. Fiberglass or plastic tanks are sometimes preferred for their chemically inert properties, light weight and ease of installation. Plastic pipes may be sealingly connected around openings in the walls of such tanks by heat fusion, solvent welding, or gluing, depending on the type of materials at the tank-pipe interface. However, unlike properly embedded concrete tanks, underground fiberglass or plastic septic tanks have relatively thin walls and a low weight-to-volume ratio that makes them more susceptible to movement with shifts in soil or changes in the watertable, and eventual dislodging of connected pipes and leakage.
Alternatively, plastic pipes have been be sealed in the openings of plastic tanks by flexible plastic gaskets. For instance, U.S. Pat. No. 4,663,036 to Strobl, Jr. et al. discloses injection-molded plastic seal of a pliable low density polyethylene or polyolefin copolymer, having an annular section with radial ribs that snap-fit into the opening of a plastic septic system drop box. A frustoconical section projecting inwardly from the annular section forms a reduced diameter opening that engages the external surface of a pipe inserted into the drop box. Blade sections at spaced locations about the angular intersection of the annular and frustoconical sections are slanted from radial alignment to provide additional tensioning and stiffening. As the pipe is inserted through the seal, the frustoconical section stretches outwardly to the pipe diameter as the blade sections slant further toward the inner surface of the annular section. Fully inserted, the three portions become highly compressed with substantially no residual resilience. Consequently any movement of the tank relative to the pipe due to any shifting of soil may cause the seal to leak. Such a seal would not meet a user""s minimum leakage requirements for a residual resilient connection between the plastic pipe and the tank such as set forth in ASTM Standard Specification C-923. In addition, the molds required for injection molding a seal of such a configuration are relatively complex and inherently expensive.
Accordingly, it is an object of the invention to provide a novel and improved resilient gasket suitable for use in fiberglass and plastic septic tanks, which positively seals the connection between a plastic septic tank and a plastic pipe against leakage, and which retains a flexible seal under conditions of movement due to shifting soil and changing water table.
Another object of the invention is to provide a septic tank gasket which is easily installed in and existing septic tank, and which is durable and resistant to corrosion.
Still another object is to provide a resilient gasket having a configuration which can be injection molded with a relatively simple and inexpensive mold.
A further object of the invention is to provide a gasket suitable for after-market installation in a septic tank fabricated without an appropriate pipe opening.
These and other objects, novel features and advantages of the invention are accomplished with a flexible gasket configured for connecting a plastic or fiberglass pipe in fluid communication with a plastic or fiberglass septic tank. The gasket is an integrally molded elastomer having an annular base with a flange portion and a keeper portion each extending outwardly from opposite sides forming with the base a continuous groove for sealing around the periphery of the tank opening. The flange portion provides a mass around the outer surface of the opening for adding stability in the gasket as the pipe is being installed; and the keeper portion tapered axially for enabling the gasket to be pushed into the tank opening and snap-fitted into position against the inside surface of the tank wall. A web portion extends inwardly from the middle of the base portion and terminates in a toroidal portion. The web portion provides a primary sealing function of the gasket, and the toroidal portion provides a secondary sealing function. As the pipe is being installed, the web portion is tightly compressed between the base and the outer surface of the pipe, whereas the toroidal portion is pushed inward and resiliently compressed between the outside surface of the pipe and the keeper portion. The added pressure produced by the toroidal portion significantly strengthens the total seal while retaining residual resilience to allow relative movement of the tank and pipe.
The foregoing features and advantages of the invention will be come more apparent from the following description when taken in conjunction with the accompanying drawings.